The Federal Security Service, Russia's main domestic security agency, said Vygovsky had contacted Russian aviation and space experts and offered them cash for sensitive information on prospective designs.

The agency said Vygovsky was arrested in Crimea while giving cash to a Russian man for the information. It said Vygovsky was planning to sell the data to an unspecified nation.

Ukraine's Foreign Ministry condemned the verdict as unfounded and called for Vygovsky's release.

Russia and Ukraine have remained locked in a tug-of-war following Moscow's annexation of Crimea and support for insurgents in eastern Ukraine.